The present invention is directed to novel polymeric compositions containing pendant functional groups. The polymers are useful for a broad range of water treatment applications. They can be used to control the formation and deposition of scale imparting compounds in water systems such as cooling, boiler, gas scrubbing, and pulp and paper manufacturing systems. They will also find utility as corrosion inhibitors, as well as functioning as chelating agents for various metallic ions in solution.
As described comprehensively in U.S. Pat. No. 4,497,713, scaling and corrosion in cooling waters is a major problem. The term "cooling water" is applied wherever water is circulated through equipment to absorb and carry away heat. This definition includes air conditioning systems, engine jacket systems, refrigeration systems, as well as the multitude of industrial heat exchange operations.
In a cooling water system employing a cooling tower, water is circulated through the heat transfer equipment and subsequently cooled by evaporation of a part of the circulating water as the water is passed over the cooling tower. By virtue of the evaporation which takes place in cooling, the dissolved and suspended solids in the water become concentrated. The circulatng water becomes more concentrated than the make-up water due to this evaporation loss.
The make-up water employed for recirculating systems is obtained from surface or well water sources. These waters normally contain a variety of dissolved salts, the abundance and composition of which depend on the source of the water. Generally the make-up water will contain a preponderance of the alkaline earth metal cations, primarily calcium and magnesium, and sometimes iron, and such anions as silicate, sulfate, bicarbonate, and carbonate. As the water is concentrated by the evaporative process, precipitation of a salt will occur whenever the solubility of the particular cation/anion combination is exceeded. If the precipitation occurs at a metal surface, and adheres to it, the resultant deposit is referred to as scale. Some of the factors which affect scale are temperature, rate of heat transfer, water velocity, dissolved solids concentration, cycles of concentration, system retention, and pH of the water.
Preventing the corrosion and scaling of industrial heat transfer equipment is essential to the efficient and economical operation of a cooling system.
Excessive corrosion of metallic surfaces can cause the premature failure of process equipment, necessitating downtime for the repair or replacement.
In addition, the buildup of corrosion products on heat transfer equipment impedes water flow and reduces heat transfer efficiency, thereby limiting production or requiring downtime for cleaning. Reduction in efficiency will also result from scaling deposition which retards heat transfer and hinders water flow.
Scale can also cause rapid localized corrosion and subsequent penetration of metallic surfaces through the formation of differential oxygen concentration cells. The localized corrosion resulting from differential oxygen cells originating from deposits is commonly referred to as "under-deposit corrosion."
With regard to boiler systems, and as described comprehensively in U.S. Pat. No. 4,288,327, the formation of scale and sludge deposits on boiler heating surfaces is the most serious water problem encountered in steam generation. Although external treatment is utilized in an attempt to remove calcium and magnesium ions from the feed water, scale formation due to residual hardness (calcium and magnesium salts) is normally experienced. Accordingly, internal treatment is necessary to prevent, reduce, or inhibit formation of the scale-imparting compounds and their deposition.
Other scale-forming species (phosphate, sulfate, and silicate salts, for example) can form complex insoluble salts, depositing as boiler scale.
Therefore, there is a need in industrial water treatment for materials which can prevent or inhibit the formation of scale and deposits on heat transfer surfaces in boiler systems, and the like.